回文数判断(Leetcode)

problem address

Determine whether an integer is a palindrome. An integer is a palindrome when it reads the same backward as forward.

Example 1:

Input: 121
Output: true
Example 2:

Input: -121
Output: false
Explanation: From left to right, it reads -121. From right to left, it becomes 121-. Therefore it is not a palindrome.
Example 3:

Input: 10
Output: false
Explanation: Reads 01 from right to left. Therefore it is not a palindrome.
Follow up:

Coud you solve it without converting the integer to a string?

前面了两种方法是取巧了，另外不用转化成字符串怎么做？
可以将数字每位上取出来然后再进行比较

class Solution:
    def isPalindrome(self, x: int) -> bool:
        # return list(str(x)) == list(reversed(str(x)))
        # return str(x) == str(x)[::-1]
        if x < 0:
            return False
        beg = 0
        s = str(x)
        beg, end = 0, len(s) - 1
        while beg < end:
            if s[beg] == s[end]:
                beg += 1
                end -= 1
            else:
                return False
        return True

class Solution:
    def isPalindrome(self, x: int) -> bool:
        if x < 0:
            return False 
        elif x == 0:
            return True
        l = [] 
        while x != 0:
            l.append(x%10)
            x = x // 10 
        return l == list(reversed(l))